Electrical heating appliance



ug. 15, 1933. A 1 KERCHER 1,922,440

ELECTRI CAL HEAT ING APPLIANCE Filed Aug. 18, 1930 lll xu1.&11111111111111111111111111 INVENTOR. r/U// Here/7er ATTOR Patented Aug. 15, 1933 y UNITED STATES vPA'rErVr OFFICE ELECTRICAL HEATING `AlarLmiwcl:

Arthur J. Kercher, Berkeley, Calif. K Appliation August 1s, 1930. serial No. 475,875

' 5 claims. (o1. 20o-13s) This invention relates generally to appliances for electrically heating various mediums, and is particularly adapted for use in conjunction with electrical water heaters. It also relates to the construction of thermostat or temperature re'- sponsive switches.

It is an objectl of the invention to devise a novel appliance of the above character which will have provision for the automatic control of the current supply inaccordance with temperature changes. The appliance as will be presently described is characterized by simplicity of structural features, by ease of manufacture and assembly, and by the fact that it can be readily l5 adjusted and serviced when in use.

1t is a further ob'ject of the invention to devise a thermostat switch which will be relatively sensitive to temperature changes and in which the 'electrical contacts will be operated in a positive manner.

Further objects of .the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawing. It is to be understood that the appended claims are to be accorded-a range of equivalents consistent with the state of the prior art.

AReferring to the drawing:

Figure 1 is a side elevational view in cross section, illustrating an appliance incorporating the present invention.

Figure 2 is a cross sectional view taken along the line 2 2 of Fig. 1.

Figure 3 is a cross sectional detail taken along the line 3--3 of Fig. 1.

' Figure 4 is an end view o f the appliance shown in Figs. 1 and 2, with the cover of the head-like mounting removed.

Figure 5 is a diagrammatic view illustrating operation of the thermostat switch. i

The appliance as illustrated in the drawing consists of an electrical heating element 10 which is preferably elongated in form, and which has its one'end secured to a head-like casing or mounting 11. While various sizes of electrical heating elements can be employed, the particular construction shown is similar to that illustrated in Figs. 2.and' 3 of Kercher and Hicks Patent No. 1,671,592 granted May 29th, 1928. It can be described briefly as comprising a sealed tubular sheath 12 made of suit-,- able metal, such as copper, within which a coil 5 resistance conductor 13 is disposed. To provide with an equivalent liquid tight joint suitable insulation a plurality of refractory insulating tubes 14 are strung upon conductor 13. 'Ihe terminal wires 15 for conductor 13 extend through one end of tubular sheath 12,` while the other end of the sheath is sealed. Mounting 11` can be conveniently made of a suitable metal casting, and is provided with a portion 16 -of reduceddiameter adapted to be secured to the wall 17 of a water tank or other liquid container. 'In practice it is convenient 65 to provide portion 17 with a pipe thread 18 which can be screwed into the tank or container wall 17 to form a liquid tight connection. The inner e`nd of portion 16 iswelded or provided adjacent portion of sheath 12.

The enlarged outer portion of mounting 11 is head like in form, andfit is preferably hollow to accommodate the thermostat switch to be presently described, and to accommodate the conductors for making an electrical connection with yheating element 10. Thus one convenient form for the interior of mounting 11 is to provide that portion of the mounting- Within portion 16 with a cylindrical bore .21, and the 80 outer enlarged portion of mounting l1 withv an enlarged cavity 22. Ordinarily the interior mounting 11 is closed by a suitable removable cover plate 26.

The thermostat switch and its associated parts preferably consist of a metal tube 27, adapted to be telescopically disposed within the cylindrical bore 21. A metal plate 28 is secured to the outer end 'of tube 27, and this plate serves to carry certain terminal .connectors and other parts to be presently described.

The electrical contacts for 4controlling the supply of current tothe heating element 10 consist vin this instance of a movable contact 29, carried upon one end of the movable arm .31, and a relatively stationary contact 32. Stationary contact 32 is carried by a member-33 extending outwardly from plate 28,` and which is mounted upon L shaped member 34. Member 32 is bent to form an extending portion 100 which is provided with a suitable connection terminal 36. One portion of a conductor bar 37 is interposed between plate 28 and laterally bent portion 34, and is likewise providedwith a terminal connector 39. A bolt 41 passes 105 through plate 28, bar 37, and member 34, to securely clamp these parts together. Insulating strips or washers serve toinsulate portion 34 from conductor bar 37, and to also electrically insulate these parts with respect to metallic with the 70 plate 23.4. Other terminal connectors 43 arej mounted upon plate 28 and are electrically insulated from the same. The inner end of bolt 41 serves as a stop to limit opening movement of contact 29. e

For eiecting movement of contact 29 responsive 'to temperature changes, I have illustra'ted :means consisting of a pair of bimetallic strips 46'andv 47 which are adapted to ex in response to temperature changes. Strips or this character are well known in the art and are formed of laminof dilerent metals, braced, welded or otherwise secured together, and having diierent temperature, coeicients of expansion.

In order to mount strips 46 and 47, the inner @mi of tube 27 is provided with a plug 4a made limetallic strips 46 and 47 areextended can be made clear by reference to Fig. 1. 'view it will be noted that the end of arm 31 oi suitable material -having `relatively good heat conductivity, such as metal, and which is slotted toreceive the inner ends of strips 46 and 47. The -strips are locked within-plug 43 by means of rivet pin 49, which also serves to lock the plug to tube 27.- Apertures 5 1 are formed in plug 48, through which the terminals 16 from the resistance conductor 13 can extend. Tube. 2.7 is also "shown provided with slots 52, communicating with opposed channels or grooves 53 .in mounting vil, whereby the terminal conductors 16 can be extended to the interior of tube 27, through channels 53, into the enlarged cavity 22.

to the outer side of plate 28, where they cooperate in a novel manner to conjointly effect operation of arm 3i. Thus the outer end of bimetallic strip 46 is provided with a laterally bentfportion 56 and interposed betweenthis portion and the opposed outer end lof strip 47 there is a pivoted toggle triage 57. f

The preferred construction of toggle bridge 57 1n this remote from contact 29 is provided with a por.- tion 53 of enlarged width. Portion 58 is provided with a plurality of aligned apertures 59 within which studs 61 are disposed. The studs are ,preferably of metal and are. insulated from. metallic portion..58 bysuitable means such as the'.

apertured insulating strips .'62. Aligned pivot pins 63 project from studs 6i,` and' the plane of the points of .these-pins is substantially at right angle vtc the arm 3l and substantially at right angle to theI directions of iiexing of bimetallic strips 46 and47. Mounted upon the outer end of bimetallic strip 47 there is a portion 64 formed with a groove 66, within which the pivot pins 63 on one side of bridge 57 engage. The pivot pin-63upon the other side'of bridge 57 engages in a recess 67 providedfin the head 68 of.. a plunger 69. Plunger 69 is preferably adjustably mounted upon laterally bent portion 56, for a purpose `Whiclr is to .be presently explained.

Thus it is shown yslidably disposed within a sleeve 7l, and this ,sleeve in turn isdisposed within. a slot 72 formed in laterally bent portion 56... .An

Aeccentric or cam 73 is formed upon the inner end of sleeve 71, while the outer end of the sleeve is iorrnedwith a nnger engaging portion 74. A' compression spring 76serves to normally bias plunger 69 inwardly .upon the .corresponding -pivot pin 63. An abutment member 77 is secured to laterally bent portion 56, and servesto `retain sleeve 71 withinslot 72, and also serves toengage the surface of eccentric 73.4 It is evident that by maintaining, the surface of eccentric 73 in contact with abutment 77, `rotation of sleeve 71 Maggio through 180' willserve to cohtinuously vary the position of plunger 69 with respectto bimetallic tor 39, 4and, the other to the other terminal connector 43. Terminal connector 39 is connected to'movable contact 29 byflexible conductor 79. Thus, since terminal connectors 43 are directly electrically connected together', the contacts 29 and 32 are connected in series with the heating element 10. l

To describe operation of the appliance 'it will be presumed that it is. mounted upon a wall 17 of a water tank, to form an electrical Water supply heater. If the water .adjacent element`10 is relativelyA cool contacts 29 and 32 are closed and current is supplied to the heating element. As the-Water surrounding the element 10 becomes heated, the temperature of portion ,16 of the mounting 11 is also heated and heat is conducted to bimetallic strips 46 and 47 through tube 27 and through the metal v yplug 48. Strips 46 and 47 are so'disposed that they tend ,to flex in opposite directions responsive to like changes in temperature, and therefore when they are heated to a` certain predetermined degree their iiexing imposes a turning couple upon toggle bridge 57, serving to lrotate this bridge -to move arm `31 in a direc- .tion to open contact 29.

the water in contact with element 10 becomes cool, either by replacement of. the hot water ,with cooler water, or by dissipation of heat, bi-

Assuming now that l metallic strips 46 and 47 are likewise cooled,

and they then serve toimpose a turning couple upon bridge 57 in the opposite direction to effectl closing of contact 29.

It is characteristic of toggle bridge 57 that its movements are relatively rapid, thus veffecting. rapid and positive opening and closing movements ofcontact 29. This characteristic is due to-the fact that it functions as a toggle, due to. the bias which is imposed upon it by virtue of compression spring 76. This -.toggle eil'ect can be better explained by reference to Fig. 5. In this View toggle bridge 57 has been indicated diagrammatically, and the bias imposed upon it by virtue of compression spring 76 has been represented bythe force components 1 and 2.

Assuming a closed position of contact 29, corresponding to the 'solid lines in Fig. 5, it will be noted that-force components land 2 are slightly out 'ofvline with the result that lin such positionoiLbridge 57, the bridge is. subjected to an -appreciable turning couple tending to-hold the lcontacts closed.v Assuming now that bimetallic .strips 46 and 47` areheated to a sufcient tem- .perature to effect openingy of contact 29, the

force components imposed upon bridge 57 by exing of strips 46 and 4,'1.. can be represented by components 3 and 4.. These components 3 and 4. must rst overcome the turning couple created bycmnponents 1 and 2 after which bridge 57 moves past dead center position to the position indicated in dotted lines in Fig. 5 corresponding to open position of contact 29. In

servicing.

this second position shown in dotted lines in Fig. 5, the bridge is likewise under an appre ciable turning couple by virtue of components 1 and 2, so that this couple must likewise be overcome when strips 46 and 47 are cooled to ex in an opposite direction. Thusfor each movement of bridge 57 to effect opening or closing movement of contact 29, the bridge moves past a de ad center position. This mode of operation results in rapid and positive opening and closing of the contacts.

In addition' to the advantages of my invention which have been pointed out above, the positive action of the contacts is not effectedl at a sacrifice of sensitivity. This characteristic is by virtue of the fact that bimetallic strips 46 and 47 act additively in opposite directions upon the toggle bridge 57. Thus the strips need not be of excessive length, and they may be relatively rugged in construction to make possible reliable operation over long periods without frequent Itis apparent that adjustments of the angular sett-ing ofvsleeve 71 makes it possible to effect opening and closing of the circuit at different points along a Vsubstantial temperature range. Thus when the device is incorporated in an electrical hot water supply heater, sleeve 71 can beset at such an angular position as to maintain the source of supply of hot Water at a prea pair of bimetallic strips, one end of each of said 'strips being relatively xed and the other ends being free and adapted to move in opposite directions in response to a change in temperature, a toggle bridge member interconnecting the free ends of said bimetallic strips and adapted to be rocked in accordance with the relative movement between the strips, a contact carrying arm mounted 'on said toggle bridge, and means for varying the inclination of said bridge relative to the ends of the bimetallic strips on which it is mounted, thereby altering the operation of said switch. V x

2. A thermostat control device comprising a thermoresponsive switch, said switch comprisingy a pair of bimetallic strips, one end of each of said strips being relatively xed and theV other ends being free and adapted to move in opposite directions in response to a change in temperature, a toggle bridge member interconnecting the free ends of said bimetallic strips and adapted to be rocked in accordance with thel relative movement between the strips, a contact carrying arm mountedon said toggle bridge, and eccentric means for moving the point of support of one end of said toggle bridge to eiect a corresponding variation in the operation of said switch. i

3. In a device of the character described, a

pair of bimetallic strips adapted to ex in re- 'strips' extending in the same general direction,

a laterally extending portion secured to the free end of -one of said strips, a switch arm, and a toggle bridge member secured to one end of the switch arm and interconnecting said laterally extending portion and the free end of the other bimetallic strip, said strips being adapted to flex toward or away from eachother for like changes in temperature.

5. A thermostatic' control device comprising a tubular member, a pair of bimetallic strips ex' Vwo rocking of said' toggle 

